The present invention relates generally to a simple and low-cost electronic control to improve the humidity removal capability of fixed speed air conditioners and heat pumps operating in cooling mode, using the existing blower motor and without the need to install a variable speed drive, or complex control and sensor logic.
It is well known in the art that slowing down the rotational speed of an evaporator blower of a vapor-compression cooling system (thereby reducing the air flow) will lead to lower evaporator temperatures and improved humidly removal and that increasing the speed of the evaporator blower (thereby increasing the air flow rate), will lead to an increase in the evaporator temperature and therefore higher efficiencies. It is this principle that is used in more expensive and higher efficiency air conditioners and heat pumps that are fitted with variable speed blowers. Thermodynamically, an increase in the Coefficient of Performance in cooling (referred to as COPc), will occur if the evaporator temperature is increased (for a constant condensation temperature). The COPc is the cooling capacity at a particular operating condition (indoor and outdoor temperatures and humilities) divided by the power consumption at those conditions. Likewise, the lower the temperature of the evaporator coil, the greater the dehumidification and moisture removal.
The basic concept that the higher the evaporator temperature, the greater the performance, goes all the way back to the fundamental Carnot cycle and the basic principles of thermodynamics. There are numerous references to this well-known fact, such as U.S. Pat. No. 5,303,561 which states in column 2, lines 13-15 which states “this is due to the fact that a highly efficient air-conditioning system nominally operates at higher evaporator coil temperature . . . ” That patent proposes the use of a continually variable blower motor to modulate the blower speed using a “integrated drive and variable speed motor” (col. 6, lines 21-22), and this approach in one form or another is used along with complex control logic to establish the optimal blower speed for the desired temperature and humidity in the building. This known system uses a combination of indoor air temperature, indoor humidity and outdoor air temperature for selecting the speed of the indoor evaporator blower motor.
Likewise U.S. Pat. No. 6,282,910 discusses using an AC induction blower motor along with a variable speed drive, where for full speed operation the alternating current power is directly coupled to the motor at nominal line frequency and bypasses the inverter, while for reduced speed operation, the output of the inverter is used to reduce the speed of the blower. This patent also discusses the benefit of reduced air flow for reducing the humidity (see col. 5, lines 5-8). However, while using the existing alternating current (AC) induction motor, this known approach uses a continuously variable speed drive inverter to vary the speed of the blower motor.
Others have proposed to modulate the compressor speed, such as disclosed in U.S. Pat. No. 7,946,123, but these methods also require variable speed drive inverters or different compressors to implement in a retrofit configuration and are thus costly and impractical for retrofit applications. Likewise, U.S. Pat. No. 7,739,882 discloses a variable speed control system for use with a variable speed compressor.
U.S. Pat. No. 7,191,607 discusses a speed control that selectively operates the fixed speed blower motor to slow the speed of the blower for dehumidification. However, this capability is used to slow the speed of the blower motor only in the initial stages of the cooling mode, typically the first 5 to 7 minutes. While a humidistat for the detection of humidity is proposed, this humidity measuring device is used with a motorized outside damper and is not used to adjust the speed of the evaporator blower motor. This is a much more expensive and complex approach because it requires the use of an outdoor air supply adjusted by a motorized damper which is controlled by a humidistat. Furthermore, nothing is suggested about decreasing the speed of the blower in response to feedback from a humidity sensor or humidistat, even though the system of the '607 patent uses a humidistat. The humidistat shown in the FIG. 4 of that patent shows the humidistat in series electrically with the circuit to provide damper control of outside air introduction. There is no teaching of operating the blower at maximum speed initially, while waiting a delay period, so as to obtain an better mixed air humidity reading from the humidity sensor, prior to making any decisions based on the humidity readings of the sensor. Col. 4, line 63 through col. 5, line 1, of that patent states that: “the time delay circuit 48 is programmed so that the speed controller 46 runs the blower 38 al first, lower speed for a predetermined ‘delay’ period once the blower 38 is first turned on at the beginning of an air conditioning cycle. When the delay period elapses the blower 38 is run at the second, higher speed for the remainder of the cycle.” In other words, the blower operates at an initial slow speed, regardless of the sensory output of the humidistat, for a delay period of time and then operates at a second higher speed thereafter, regardless of the sensor readings from the humidistat.
As is well known in the art; blower motors used in many air conditioning and heat pump systems typically utilize fixed speed blowers with a ability to manually select one of many multi-speed taps on the blower motor, while the more expensive and higher performance air conditioners and heat pumps many times use Electronically Commutated Motors (ECM) that can be used to provide continuously variable speed control to maximize the COPc. In addition to our realization that we can use any type of multi-speed-tap motor along with the invention described in our related patent application (Ser. No. 13/538,441 filed Jun. 29, 2012, by Robert Paul Roth et al and entitled “Retrofit Device and Method to Improve Vapor Compression System Performance by Dynamic Blower Speed Modulation”) to improve COPc at a much lower cost, we have also realized that we can use the variable speed taps of these low-cost blower motor to improve humidity removal rate from the conditioned air when necessary. And do so with an inexpensive and easy to retrofit approach.
We have realized that instead of using the more expensive continuously variable speed blowers to achieve variable speed humidity control by incorporating a humidistat, also referred to as a humidity sensor, to provide some type of continuous speed variation of the variable speed ECM motor, we are simply using the slowest possible fixed speed. of the low cost multiple speed tap motor when the feedback from the humidity sensor or humidity switch indicates high humidity (at or above a high humidity threshold), and some other speed when the humidity is not above the high humidity threshold. The other speed can be manually selected by the technician installing or servicing the air conditioning or in our preferred embodiment the other speed can be selected by a control logic that will maximize performance when humidity is not an issue.
We have also realized that, to obtain the best humidity reading by the humidity sensor or switch located in the return air flow section of the indoor air handling unit of the air of the conditioner, the low-cost multiple speed tap blower motor should be operated at the highest speed possible for an initial delay period and then take the humidity reading before any blower motor speed changes are made.
It is well known in the art that the lower-cost multiple speed tap motors are normally used as a fixed-speed blower, where the multiple different winding combinations (different speed taps), allow the air conditioning installer or maintainer to select from an assortment of fixed speeds from the same evaporator blower motor (depending on the wiretap that is activated) to best balance the air flow for a particular installation. In a conventional application, once the speed is selected, the evaporator blower operates at this speed setting whenever the motor is activated. The installer typically has the option of selecting low, medium, or high speed for the blower's operation, while some blower motors even have five or more speed selections. Once selected, typically by placing a power-lead on a low, medium or high speed tap on the motor, the evaporator blower speed will then operate at this speed whenever it is powered on. The present invention uses the same multi-speed taps to provide dynamic variable speed adjustments, based on the humidity in the conditioned structure, as determined by the humidity of the air being returned to the suction side of the evaporator blower assembly. It is also common for the installer or maintainer to select a different speed tap for furnace heating when compared to cooling by the air conditioner.
The present invention uses the exact opposite control logic on startup of that used in the system disclosed in the above-mentioned U.S. Pat. No. 7,191,607. That is, in the present invention, when the air conditioner is started and the evaporator blower is activated, the blower motor speed is set to the maximum speed for the initial startup rather than the slow speed. We have found that this approach more effectively circulates the air in the structure, so that a more accurate humidity measurement at the inlet to the blower can be measured. The humidity is detected by a humidity sensor either located directly on the control board of the invention or remotely via a short cable to allow the humidity sensor to be placed in the return airflow.
The present invention is elegant in its simplicity and its ability to provide dramatic improvements in moisture removal when the air conditioner or heat pump is operating in cooling mode. Furthermore, it provides this humidity reduction, without any need to replace the existing thermostat based control system, the existing evaporator blower motor, to or add any complex, costly and large inverter or other speed controller system. Due to its simplicity, it can easily and quickly retrofitted into exiting air conditioning and heat pump cooling systems, even when a separate heating system is present. No additional control wiring needs to be used and the humidity sensor is wired to only the control board of the present invention. For systems where the air conditioner or heat pump is coupled with a furnace, that is the evaporator is located in the furnace assembly and the same blower motor operates for furnace heating and vapor compression (AC or heat pump) operation, a separate blower motor power lead for heating operation is typically provided and the invention described herein is bypassed. However, when only a single set of power leads to the blower are provided for both heating and cooling, the present invention can still be successfully utilized without modification even though invention receives power only from the leads supplying the blower motor and is not in any other way connected to the control system or thermostat without additional sensors or devices, and therefore does not know if the heating or cooling capability is being utilized. When the blower motor is operating to deliver heated air into the conditioned space, and the return air is of high humidity (above the HSP threshold), the control board of the present invention will lower the air flow and thereby increase the temperature of the heated supply air. While not providing any actual moisture removal in this air heating situation, this is a favorable response, since humidity (i.e., dampness), lowers the occupant's comfort level, and supplying warmer air will mitigate this issue. Of course, it is also well known that while the specific humidity has not changed, that is, the mass of moisture in a mass of dry air has not changed, the relative humidity has decreased, due to the ability of warm air to hold more moisture relative to cold air, making the relative humidity decrease. Therefore, the simple control board of the present invention operates with only the humidity measurement and power from the blower motor leads and can be used without regard to when the blower motor is operating in cooling or heating.
Another benefit of our invention is the simple installation it affords, and the ability to use the existing blower motor, thermostat and control system which activates the cooling system.